.
I submit that bigger microlenses don't reduce picture noise even though they do allow greater sensor efficiency. What does reduce picture noise is a greater full-well capacity at each photosite.

Have you ever wondered why ISO 100 is the lowest setting for most DSLRs? If you could significantly increase the number of photons that could be counted at each photosite (i.e. increase the full-well capacity) you could drive the noise level down by setting, say, ISO 25 and capture more light (thereby counting more photons) by using a slower shutter or a faster aperture.

It would seem that what gives full frame sensors their better noise characteristics is that more silicon can be devoted to storing the signal from the detected photons rather than any increased size of the photodiodes themselves.

Bob, I understand that micro-lenses just reduce the "waste" you get from the borders between photocells: They let you collect all the light that theoretically falls on the area of a photocell.
So they cause more photons to hit the cell (=sensitivity) but cannot increase the well-capacity (s/n-ratio). So all-in-all I assume you're right...

Bob, I understand that micro-lenses just reduce the "waste" you get from the borders between photocells: They let you collect all the light that theoretically falls on the area of a photocell.So they cause more photons to hit the cell (=sensitivity) but cannot increase the well-capacity (s/n-ratio). So all-in-all I assume you're right...

Thanks for that, Thomas, and good to see you back on the forum after your short break.

I have started thinking seriously about well-capacity because the new EOS 40D, while it has a lot of very desirable new functionality, seems to have demonstrated that improvements in sensor noise seem almost to have plateaued. There seems to be only a small improvement, which given the increase from 8 to 10 MP is still neat. Do you know if the Nikon sensor in the D300 done any better in comparison to the D200?

Bob, I'm not going to have one of those shiny new Nikon-toys in my sweaty little mitts for a very long time, so I'm only speculating and extrapolating from the many tests (of older bodies) so far:
-------Disclaimer: all the following is my personal opinion------
Yes, noise and sensitivity of sensors of a given format are plateau-ing more or less. So perhaps with a 20% increase of pixels (from 8 to 10 MP or 10 to 12 MP) the manufacturers may manage to keep the s/n-level at the same level, but that will be hard to tell unless you shoot test-graphs where you can nail any increase in noise-reduction and smearing.
Sadly I believe that the DSLR-manufacturers will go the same route as everybody with the P&S, just to stay in the Megapixel race.
So we will ultimately only see an increase in resolution under optimal lighting conditions with reduced effective resolution under low-light.
But - why not? If the laws of physics limits the amount of s/n-ratio you can get out of each and every photon, so be it Consequently you should spare enough change to get a 20MP FF-body and live happily ever after

Hi Bob, that's an interesting question about the lowest sensor ISOs... there'll almost certainly be some semi-conductor explanation for this, so next time I manage to collar a chip engineer, I'll ask them!